1. Field of the Invention
The present invention relates to a brushless DC (Direct Current) motor drive circuit. More particularly, the present invention relates to a brushless DC motor drive circuit having a transient current suppression circuit to suppress the transient current caused by a motor commutation process.
2. Description of the Related Art
Referring to FIG. 1, a conventional brushless DC motor drive circuit includes a power supply end 91, a voltage regulator circuit 92, a coil set 93, a Hall component 94, a control component 95, and a drive component 96. The power supply end 91 connects to a DC power source to supply a stable DC voltage to the Hall component 94 and the control component 95 while the power supply end 91 supplies a stable DC voltage to the coil set 93 through the voltage regulator circuit 92. The coil set 93 connects between the voltage regulator circuit 92 and the drive component 96. The Hall component 94 has two output ports 941, 942 connected with the control component 95 for transmitting two complementary digital command signals, that is, the commutation signals, wherein the two complementary digital command signals are generated according to the polarity position of a motor rotor (not shown). In order to control the states of a transistor Q1 and a transistor Q2 of the drive component 96, the control component 95 comprises two control ports 951, 952 respectively connecting to the bases of the transistors Q1, Q2.
In normal operation, the commutation signals generated by the Hall component 94 are transmitted to the control component 95 and transformed into a pair of complementary digital control signals such as a HIGH signal and a LOW signal. The complementary digital control signals are respectively transmitted to the bases of the transistors Q1, Q2 of the drive component 96 so as to maintain the transistors Q1, Q2 at different states and constantly switch the transistors Q1, Q2 for commutating the currents of the coil set 93 and therefore running the motor. Furthermore, an ideal operation for controlling the drive component 96 is that the transistor Q1 is at on-state while the transistor Q2 is at off-state, and, contrariously, the transistor Q1 is at off-state while the transistor Q2 is at on-state.
However, when the bases of the transistors Q1, Q2 receive the complementary control signals simultaneously, owing to the transistor characteristics namely the turn-on time of a transistor being shorter than the turn-off time thereof, an overlap time exists wherein both of the transistor Q1 and transistor Q2 are at on-state. Therefore, a transient current is occurred during the overlap time when the drive component 96 commutates the currents of the coil set 93. Referring to FIG. 2, the voltage level and frequency of the transient current is much higher than that of the normal rated current and results in a serious decrease of stability of the motor drive circuit. Besides, the high frequency of the transient current may cause sensitive elements, such as microprocessor, to suffer electromagnetic interference and be at a risk of executing error operation. Moreover, the high voltage level and frequency of the transient current also cause damage to the motor and the drive circuit thereof. Hence, there is a need for improving the motor drive circuit so as to suppress the transient current during the motor operation.
The present invention intends to provide a brushless DC motor drive circuit with a transient current suppression circuit to enforce one of two transistors having a ground connection immediately while the transistor receives an OFF command from a drive component so as to avoid both of the transistors being at on-state. Consequently, the stability of the motor drive circuit is improved, and the damage to the motor and the drive circuit thereof is effectively lowered.